Got Tree and Shrub Problems?
South Central Colorado is a great place to grow happy and healthy plants—we don’t have rampant insect or disease problems very often. However, from time to time, our customers bump into a bug or disease problem in their yards, and when they do, they drop by the shop looking for a solution. We’ve collected their questions and provided answers to these questions below.
The leaves on my maple tree have turned yellow but their “veins” are still green. It looks like it is dying—what is the problem?
Trees and shrubs sometimes suffer from nutritional deficiencies that cause their leaves to turn yellow long before fall. One very common nutritional deficiency is iron chlorosis, which manifests itself when the leaf turns yellow in between its veins, which remain green. Iron chlorosis is often caused by lack of nutrients in the soil or the plant's in ability to uptake nutrients because of high soil ph. The deficiency produces a lack of chlorophyll (the "green" in leaves). Two common approaches to treatment include (a) treating either the soil or the leaves with chelated iron or (b) adding an amendment such as compost to the soil around the plant and covering it with a thick layer of mulch. The compost will break down in the soil and increase the health of the soil. Left: Iron chlorosis in an Amur Maple shrub.
I have an odd-looking growth on the leaves of one of my Gambel’s Oak shrub. It is round and reddish. What is it ?
This growth is called a “gall” and it is caused by insects or mites, usually where lay their eggs or feed. Galls also sometimes can from an infection. Depending on the tree or shrub, galls will appear different. For example, galls can be different sizes, shapes, and colors, depending on the insect that is causing them or the kind of plant on which they appear. Some galls will appear in twigs or branches and in both deciduous and coniferous plant species. Galls are unsightly, but they don’t usually damage the plant. Galls can be prevented by using an insecticide that kills the insect or mite causing the gall. Left: Gall on Gambel’s Oak leaf.
Some of the lower branches on some of my Blue Spruce seemed to have been stripped of some of their needles. Is this due to a disease or animals?
This problem is due to either deer or rodents nibbling on the needles near the end of branches on your trees. If the stripping is low on the tree, it is likely due to rodents, such as voles. If the stripping is a bit higher on the tree, then deer are the likely culprit. This sort of nibbling can be reduced or prevented by spraying a repellent on the tree’s lower from those hanging near the ground to about 4-5’ high. Left: Stripping of needles on a Blue Spruce.
Many of the needles of one of my piñon pine trees are turning yellow and have raised black spots on them. I am concerned that this piñon is not doing well, what should I do?
Your piñon tree has piñon needle scale (PNS), which is an infestation of small sap-sucking insects that will eventually thin needles leaving only small tufts of needles at the very tips of branches. The black spots on the needles is actually a covering that protects female scale from environmental conditions. Repeated infestations can eventually kill small trees and greatly reduce the vitality of larger trees, opening the way for infestations of other insects, especially beetles, which spells doom for those trees. Here are a two tips for attempting for keeping PNS under control. First, make sure that your piñon is well-watered, especially during the dry season to keep trees from becoming even more stressed by drought conditions. Second, beginning in very late winter/early spring, observe the tree for the insects moving toward the lower trunk and branches to lay their eggs in what looks like dense masses of dryer lint or thick spider webs. Once you see migration and "lint," spray the tree, top-down, with a high-pressure sprayer, which will knock the insects onto the ground. 15-20 minutes later, rake up materials under the tree, and bag them This step will greatly reduce the number of PNS infesting your piñon. Unfortunately, you will have to repeat this process for several years to keep the infestation at bay. Third, you can apply an insecticide, such as a horticultural oil or imidacloprid (Fertilome Systemic Drench) while females are migrating down the tree. This treatment, too, will have to be repeated to effectively control PNS populations.
I’ve got cob web-like thing in one of my aspens with what looks like caterpillars in it. What is it?
You have an infestation of tent caterpillars. Each of these webs may contain up to several hundred caterpillars. Tent caterpillars can appear in both deciduous and conifer plants, and in the latter, their nests actually look like pine cones. Tent caterpillars will eventually crawl out of the web and feed on the host plant’s leaves or needles. Wind can disperse the caterpillars from plant to plant and large infestations can defoliate plants. If left unchecked for several years, tent caterpillars can kill the host plant. There are two ways to control tent caterpillars. The first is to simply remove the web from the plant before the caterpillars escape the web. Destroy the web away from the infected plant to prevent any surviving caterpillars from returning to the plant. Second, if the caterpillars have already emerged from the web and are feeding, an insecticide, like Bacillus Thuringiensis or Spinosad, must be used. Insecticides cannot generally penetrate the web and thus must be applied directly to the caterpillars themselves. Left: Enlargement of web and tent caterpillars within it on a Serviceberry bush.
Some of the leaves on my plant are all shriveled up and when I looked closely at them, I saw little pieces of fuzz on them. What’s going on?
Sounds like aphids, although these insects can be other colors than white: black, brown, gray, green, pink, or yellow, and they attack a huge variety of plants including shrubs, flowers, and vegetables in addition to trees. These bugs suck the juices out of foliage, causing leaves to shrivel or curl up. Aphids usually hide out on the underside of leaves, so if the edges of the leaves of your plants is curled under, check the underside of the leaf for aphids. The waste secreted by aphids can attract other insects, chiefly ants, and also foster sooty mold, a fungus that will cause leaves and branches to become blacken. Fortunately, aphids are easily controlled using insecticides. Sometimes spraying cold water on small infestations of aphids will even work. Left: In the center of this photograph, you can see several aphids. The “fuzz” seen on some aphid-infested plants are the skins that the bugs have shed.
The leaves on my maple tree have turned brown and brittle following a freeze. Does that mean the tree is dead?
It is not unusual for Chaffee County to experience a late winter or early spring warm up followed by a day or two of freezing temperatures. If you have a tree or shrub that has started to leaf out during the warm-up period, any subsequent frost will kill the the young leaves. Fortunately, in the case of your maple, and in many other types of deciduous trees, it will bloom a second time a few to several weeks following the killing frost.
We’ve had a very hot summer, and the leaves on my aspen are now brown and crumbly. The space between the veins of the leaves are yellow, too. What should I do?
What you’re describing is called leaf scorch. Plants are constantly losing water through their leaves or needles, a process called transpiration. If this water loss is not compensated for through rain or water, leaf scorch results. Environmental conditions that contribute to this problem include hot dry weather, high winds, and drought. Thus, it is very important that under these conditions you water your plants frequently. Keep in mind that underwatering is also a contributing factor to leaf scorch, especially in young or newly planted trees, shrubs, and flowers. Thus, make sure your watering results in a slow, deep penetration of water to the deepest roots. Left: Typical leaf scorch damage. Photo by Carol O’Meara courtesy of Colorado State University Extension
This winter, I’ve noticed that the bark on some of my crabapple trees is cracked. It seems to be mostly on the southwest side of the tree. What’s happening with these trees?
Your trees are suffering from sunscald, a condition that occurs when the cells beneath the bark are first warmed by the sun during the day and then frozen by plumeting nighttime temperatures. Primary symptoms of sunscald are bark discoloration and cracking. Young trees with thin bark are the most susceptible plants to sunscald, which is sometimes called southwest injury because the damage is usually found on the part of the trunk and limbs facing this direction (this side of the tree gets the most direct and sustained afternoon sun). To prevent sunscald, wrap the trunk with tree wrap, which you can purchase at Brady’s West. You can also paint the southwest side of the tree with a white or other light colored interior latex paint to reflect the sun’s rays (exterior latex paint contains certain chemicals that can harm the tree). Both of these methods may also prevent insect and disease from attacking the sunscalded portion of the tree.
Some of my trees have little round holes in them and on the ground below there seems to be sawdust. I haven’t seen or heard any woodpeckers, so I am wondering what’s causing these holes.
Little round holes in the trunk or limbs of the tree with bits of sawdust below those holes is a sure sign that your tree has a borer problem. Borers lay eggs in bark; when the larvae hatch, the eat into the tree causing the tree to die from the inside out. Borers include both beetles and some moths. Borers tend to infest trees that have been stressed through poor watering, bark damage from environmental sources, or weakened root systems. Thus the best way to prevent borer infestation is to take good care of your tree through proper watering and feeding, and avoid hitting it with lawn equipment. Insecticides applied to tree bark are only partially successful in killing borers. However, a systemic drench, which is applied to the soil around the tree and absorbed by roots and transported up the tree into the trunk and limbs is more effective. Trees with extensive borer damaged should be removed and replaced. Left: Borer on cottonwood. Photo courtesy of Colorado State University Extension
The tips of some of the needles on my blue spruce have turned a brownish-blue color and the tips of the needles on my Ponderosa pine appear to be yellowing. What is causing this?
In both cases, the likely problem is desiccation or massive loss of moisture from the needles. Desiccation occurs anytime that plants lose moisture faster than it be replaced by the roots. It can occur anytime of year but often occurs during the winter when the weather is cold, dry, and windy. The obvious solution is to make sure your plants are watered well—with a slow, penetrating deep watering. In the winter you should water your plants, especially those with needles, when the temperature is above 40 degrees. Try to water earlier in the day so the water has a chance to penetrate the ground prior to nighttime freezing. Another method to prevent desiccation is to spray the tree’s needles with an anti-dessicant such as WiltPruf, which will reduce water loss through the needles. We carry WiltPruf at Brady’s West.
Some of my spruce are losing their needles, although the needles at the end of the branches look healthy. The needles are particularly thin toward the bottom of the tree. Is this something I should worry about?
Yes, the problem you described may be caused by transplant shock or by lack of water, both of which can be fairly easily rectified, or it may be caused by a pesky fungus known as Rhizosphaera. In the case of transplant shock, water periodically with a root stimulator, and in the case of underwatering, obviously, water the tree regularly with a slow, deep penetrating watering. To check for the possibility of a fungus infestation, examine the needles of both green and discolored needles with a magnifying glass. If you observe rows of small black spots, you likely have Rhizosphaera fungi. This fungi can be successfully treat with fungicides.
Some of the branches and leaves on my apple tree are dying back. Some of the blossoms seem water logged. What’s causing this to happen?
These symptoms are likely to be caused by fire blight which is a bacterial problem that affects apple, pear, and crabapple trees as well as a range of other plants in the rose family. “Fire blight” is an apt name for this disease because the leaves turn brown and black, giving the appearance of being scorched by fire. Infected plants will secrete a “bacterial ooze” that is then transferred from plant to plant and blossom to blossom by insects. The disease also can be spread by rain and contaminated pruning tools. This disease cannot be cured, only managed. Chief management methods include planting blight-resistant varieties, pruning twigs and branches at least 8” below the affected areas during mid winter (disinfect pruning tools with bleach or alcohol between cuttings), and chemical spraying prior to infection. For more information, see https://extension.colostate.edu/topic-areas/yard-garden/fire-blight-2-907/.
A lot of the leaves on my aspen tree have dark spots on them. What’s causing these spots?
Aspen, cottonwoods, and other members of the popular family sometimes are infected by fungi that cause “leaf spot,” including black spot and ink spot. Although spots are unsightly, they are seldom harmful to the tree. Once leaf spots develop, they cannot be removed, but fungicidal spraying in the spring as leaf buds emerge is effective in preventing the development of leaf spot. Because moisture can help give rise to leaf spot, avoid directly watering leaves, especially late in the day. It also helps to rake up infected leaves around the base of the tree in the fall. Photo courtesy of Colorado State University Extension
The leaves on some of my trees are turning yellow. What is the problem here?
The most common cause of yellowing leaves in any plant is improper watering—either underwatering or overwatering—which stresses the plant. Check the moisture content of the soil before watering by sticking your index finger several inches into the soil about 2-4 inches away from the plant’s stem or trunk. If the soil feels dry, water the plant slowly with a deep, penetrating watering. If the soil feels moist, even muddy, then don’t water until the soil has dried out some. Most plants prefer well-drained soils. Sometimes yellowing of leaves is caused by a nutrient deficiency with the chief culprits being nitrogen and iron. Proper fertilization and regular feeding with plant foods can help address this cause of the yellowing problem.
The leaves on my hydrangea are wilting. Should I give it more water?
Wilting is always due to a water-related problem, most likely either underwatering or overwatering Dehydrated cells become weak and cannot support the weight of leaves, blooms, and flowers, causing them to droop or wilt. Obviously, underwatering or drought will cause the plant to become dehydrated and wilt. Overwatering or heavy rain will saturate the soil and prevent the roots from accessing the oxygen it needs for absorbing and transporting nutrients to the upper parts of the plant, thereby causing wilting. To determine the moisture content of your soil, you can either use a moisture probe, which are inexpensive and easy to use, or a finger test. Stick your index finger several inches into the soil about 2-4 inches away from the plant’s stem or trunk. If the soil feels dry, water the plant slowly with a deep, penetrating watering. If the soil feels moist, even muddy, then don’t water until the soil has dried out some.
I’ve noticed that some of my plants are developing really small brown and yellow spots on them. A few of the leaves have turned all yellow. I think it may be an insect problem because on one or two leaves, there seems to be tiny cobwebs.
Your plants may be infested with spider mites—super tiny insects that suck the moisture out of leaves. Because spider mites are so small (less than 1/20th of an inch), they are difficult to see. To determine if spider mites are the problem, get a piece of paper, hold it under the leaves of your plant, and shake the plant gently. If you see small specks fall onto the paper, your problem is definitely spider mites! Spider mites can be controlled naturally by “good” insects like lady bugs, or you can use an insecticide such as Triple Action, End All or Broad Spectrum.
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My bristlecone pine tree that we planted last year looked great throughout last summer and fall, but this spring many of the needles are turning brown. Is my tree dying?
Chances are that your bristlecone is, in fact, dying. When the needles at the tips of many branches in your tree turn brown, it is a sign that the tree has a serious problem. If the needles near on the branches near the trunk turn burn, there is nothing to worry about—shedding of needles in this manner is completely normal. Several of the dead or dying bristlecones we’ve observed recently have been either overwatered or planted in an area that tends to collect water (such as at the bottom of a berm).